The present invention relates generally to gas turbine engines, and, more specifically, to noise attenuation therein.
In a turbofan gas turbine engine powering an aircraft in flight, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT) which powers the compressor through one drive shaft.
Additional energy is extracted from the gases in a low pressure turbine (LPT) which powers the fan through another drive shaft. The spent combustion gases are then discharged through a core nozzle, and the pressurized fan flow is discharged through a surrounding fan nozzle for producing propulsion thrust during operation.
The core and fan exhausts are concentric with each other in the surrounding ambient air which flows outside the engine as the aircraft is propelled during flight.
The high velocity core and fan exhaust streams generate noise during operation, which is a particular problem during aircraft takeoff at high power which is in contrast with aircraft cruise at high altitude at correspondingly lower power output where noise is less of a problem but maximum engine efficiency is desired.
Noise attenuation mechanisms have been investigated for decades, but all have associated problems including corresponding additional weight in the aircraft and a reduction in engine efficiency or performance. In particular, since jet noise attenuation is typically required solely during aircraft takeoff from runways in populated communities, any noise attenuation mechanism is no longer required during the majority of flight operation during cruise. Cruise operation requires maximum engine efficiency for reducing fuel consumption.
Accordingly, it is desired to provide effective noise attenuation while minimizing engine performance and efficiency losses therefrom.